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Do not call listen() when SO_REUSEADDR is off

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For an established TCP connection, the send queue is restored in two
steps: in step (1), we retransmit the data that was sent before but not
yet acknowledged, and in step (2), we transmit the data that was never
sent outside before.  The TCP_REPAIR option is disabled before step (2)
and re-enabled after step (2) (without this patch).

If the amount of data to be sent in step (2) is large, the TCP_REPAIR
flag on the socket can remain off for some time (O(milliseconds)).  If a
listen() is called on another socket bound to the same port during this
time window, it fails. This is because -- turning TCP_REPAIR off clears
the SO_REUSEADDR flag on the socket.

This patch adds a mutex (reuseaddr_lock) per port number, so that a
listen() on a port number does not happen while SO_REUSEADDR for another
socket on the same port is off.

Thanks to Amey Deshpande <ameyd@google.com> for debugging.

Signed-off-by: Saied Kazemi <saied@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Saied Kazemi 2015-02-16 13:18:32 +03:00 • committed by Pavel Emelyanov
parent 603929cad7
commit 1b4e9058e8
3 changed files with 21 additions and 4 deletions
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1
include/sk-inet.h
View file

@ -79,5 +79,6 @@ extern int restore_one_tcp(int sk, struct inet_sk_info *si);
extern int check_tcp(void);
extern int rst_tcp_socks_add(int fd, bool reuseaddr);
extern mutex_t *inet_get_reuseaddr_lock(struct inet_sk_info *ii);
#endif /* __CR_SK_INET_H__ */

10
sk-inet.c
View file

@ -30,6 +30,7 @@ struct inet_port {
int port;
int type;
futex_t users;
mutex_t reuseaddr_lock;
struct list_head list;
};
@ -53,6 +54,7 @@ static struct inet_port *port_add(int type, int port)
e->type = type;
futex_init(&e->users);
futex_inc(&e->users);
mutex_init(&e->reuseaddr_lock);
list_add(&e->list, &inet_ports);
@ -537,10 +539,13 @@ static int open_inet_sk(struct file_desc *d)
goto err;
}
mutex_lock(&ii->port->reuseaddr_lock);
if (listen(sk, ie->backlog) == -1) {
pr_perror("Can't listen on a socket");
mutex_unlock(&ii->port->reuseaddr_lock);
goto err;
}
mutex_unlock(&ii->port->reuseaddr_lock);
}
if (ie->state == TCP_ESTABLISHED &&
@ -624,3 +629,8 @@ int inet_connect(int sk, struct inet_sk_info *ii)
return 0;
}
mutex_t *inet_get_reuseaddr_lock(struct inet_sk_info *ii)
{
return &ii->port->reuseaddr_lock;
}

14
sk-tcp.c
View file

@ -507,7 +507,7 @@ static int send_tcp_queue(int sk, int queue, u32 len, struct cr_img *img)
return __send_tcp_queue(sk, queue, len, img);
}
static int restore_tcp_queues(int sk, TcpStreamEntry *tse, struct cr_img *img)
static int restore_tcp_queues(int sk, TcpStreamEntry *tse, struct cr_img *img, mutex_t *reuse_lock)
{
u32 len;
@ -534,11 +534,17 @@ static int restore_tcp_queues(int sk, TcpStreamEntry *tse, struct cr_img *img)
* they can be restored without any tricks.
*/
len = tse->unsq_len;
mutex_lock(reuse_lock);
tcp_repair_off(sk);
if (len && __send_tcp_queue(sk, TCP_SEND_QUEUE, len, img))
if (len && __send_tcp_queue(sk, TCP_SEND_QUEUE, len, img)) {
mutex_unlock(reuse_lock);
return -1;
if (tcp_repair_on(sk))
}
if (tcp_repair_on(sk)) {
mutex_unlock(reuse_lock);
return -1;
}
mutex_unlock(reuse_lock);
return 0;
}
@ -621,7 +627,7 @@ static int restore_tcp_conn_state(int sk, struct inet_sk_info *ii)
if (restore_tcp_opts(sk, tse))
goto err_c;
if (restore_tcp_queues(sk, tse, img))
if (restore_tcp_queues(sk, tse, img, inet_get_reuseaddr_lock(ii)))
goto err_c;
if (tse->has_nodelay && tse->nodelay) {